Will.i.am's song lyrics inspired the 'Fifty Shades of Grey' book and its subsequent novels.

Author EL James has revealed the inspiration behind her raunchy writing is the Black Eyed Peas frontman.

The novelist told how she listened to his band while writing her worldwide bestsellers.

The 48-year-old woman told The Sun newspaper: ''I have songs that I write sex to. One of them is the Black Eyed Peas' 'Sexy'. That is a very sexy song.''

The track, from their 2003 album 'Elephunk', features lyrics like: ''For you I'm a fanatic, I'm an addict, your sexy antics turn me on like automatic.''

James, who has raked in a Fortune from her books, confessed her musical tastes at the launch of her 'Fifty Shades' classical album.

She added that part of the books' success was that the covers are ''discreet'', allowing fans to read them anywhere.

She said: ''I designed the covers because in my early 30s I read a lot of romantic fiction when I was slogging in and out of London on the Tube. But they had these horrible covers with women with clothes falling off.

''I hated that and I had to bend the covers back. So I designed really discrete covers so that no one would ever know it is salacious.''

She added electronic books had also helped, explaining: ''E-book readers have been very liberating for people because they can read whatever they like with no judgment.''